It’s so unique that museums and schools around the globe are hosting Venus viewing festivities - all for a chance to see our star sport a fleeting beauty mark. Even astronauts aboard the International Space Station plan to observe the event.

The drama unfolds Tuesday afternoon from the Western Hemisphere (Wednesday morning from the Eastern Hemisphere.)

Venus will appear as a small black dot gliding across the disk of the sun. As in a solar eclipse, do not stare directly at the sun; wear special protective glasses.

The entire transit, lasting 6 hours and 40 minutes, will be visible from the western Pacific, eastern Asia, and eastern Australia.

Skywatchers in the United States, Canada, Mexico, Central America, and the northern part of South America will see the beginning of the show before the sun sets. Europe, western and central Asia, eastern Africa, and western Australia will catch the tail end after sunrise. Those who don’t want to leave their homes can follow live webcasts by NASA and various observatories.

“Anything silhouetted on the sun looks interesting. Seeing Venus is extremely rare,’’ said astronomer Anthony Cook of the Griffith Observatory.

Perched on the south slope of Mount Hollywood in Los Angeles, the observatory is girding for heavy traffic Tuesday afternoon as throngs were expected to peer through telescopes with special filters set up on the lawn.

Skygazers who want the full experience are flocking to Hawaii, considered one of the prime viewing spots since the whole transit will be visible. From Waikiki Beach on Oahu to the summit of Mauna Kea on the Big Island, eclipse glasses will be given out so that people can safely see Venus crossing.

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